1. Field of the Invention
The invention relates to a clamping connection for medical equipment and apparatus, illustrated by way of an external fixator with a fixation frame made of guide rods. Fixators of this kind require a mechanical connection between the guide rods and the screws according to Schanz, which has to assure a synergetic compatibility of these system sides under all medical and functional aspects. A direct access to a multi-axes and unlimited movability with an internally tension-free, point-precise and solid coupling of guide rods of the fixation frame and of the screws according to Schanz is the central criteria for such clamping connections.
2. Brief Description of the Background of the Invention Including Prior Art
The requirements to be imposed on such a coupling result also predominantly from the medical indication of the external fixator. Thus, the external bone fracture treatment with screws according to Schanz is indicated in case of a I.-III. grade open fracture, since the external bone fracture treatment represents a quick and in particular minimally invasive and thus biological method, which additionally iatrogenically traumatizes and injures as little as possible the all decisive remaining vascularization of the damaged limb.
Since the osteosynthesis method of the external fixator in addition allows continuously available inter-fractural interventions such as compression, distraction, neutralization and dynamization of the repositioned fracture, the osteosynthesis is initially considered far more than only an alternative because of the remote position relative to the fracture of the stabilizing elements and because of the minimized invasiveness.
Indispensable constructive and functional requirements are derived therefrom for the external fixator.
The phase of the consolidation of the bone fracture requires initially an absolutely immobile retention of the repositioning result, since motions of the fragments lead to further soft tissue injuries and vascularization injuries. This is initially also possible with a fixator construction which contains internal tensions and is neutral in its sum. However, these system-internal forces begin to generate effects in the course of the treatment, which are primarily noticeable at the bone contact zone of the screws according to Schanz. Tension-induced interferences of the osseous microcirculation effect local bone resorption up to the sequestration with a consecutive loosening of the screws according to Schanz and obligatory and perpetualizing inflammation reaction as a pacemaker from a soft tissue infection up to osteomyelitis. Furthermore, a loss of the anchoring of the screw in case of a generally not yet bone-consolidated fracture is also associated with a failure of the osteosynthesis.
The external fixator of this kind has to allow in addition a pressure stimulation by a dynamization with a partial abandonment of the strictly axial fixation components for a procedural acceleration of the interfractural configuration. The two qualities however cannot be reliably realized without a reliable starting position of an internal, tension-neutral primary fixation. Also other procedural bone position changes or bone position corrections are subject to adequate requirements for the external fixator.
The constructions known in the art meet these requirements however only to an insufficient degree. Additional public and controversial concepts relating to a change in procedure toward an internal osteosynthesis after soft tissue consolidation or the use of an external fixator as an initial and definite osteosynthesis method show this.
Mechanical clamping connections of components and of component surfaces in a synergetic incompatible constellation are the prevailing state-of-the-art also in connection with medical equipment and apparatus of completely different dimension such as, for example, operating tables. Thus, various devices of the operating table function with shape-matching profiled couplings for the purpose of a preoperative positional manipulation of the patient, where the profiled couplings are furnished with an extremely coarse thread or subdivision based on the potential mass-determined requirements. The thereby unavoidable coarse positional offset of the two coupling sides causes incompatible malpositionings of the patient. A desirable sensitive and delicate, precise primary adjustment, as well as in particular also necessary acute changes or corrections during the operation, are therefore not possible. The inadequate provisional measures employed as countermeasures mean not only widely applied practical disadvantages of the operational handling, but are in addition not acceptable as a matter of principle.
The requirement for a point-precise and internally force-neutral fixation and defixation under minimal closure torques and opening torques, as well as simultaneously minimized closure paths and opening paths, holds therefore for clamping connections of medical instruments, medical equipment, and medical apparatus of the recited kind, wherein the general requirements for low proper mass and construction size, for simplicity and durable functional reliability, low wear or practically wear free, for biologically lasting compatibility as well as clinical unproblematic capability of manipulation continue without limitation.
The very sensitive and central problem, which has hitherto been completely unsatisfactorily treated and/or neglected in connection with these medical equipment and apparatus, thus continues to exist in the apparently unresolvable goal conflict on the side of the equipment relating to the physical connection between force and path; in the present case especially in connection with a coupling-forming static pairing of two mechanical components solely by their surfaces.
A force-matching-dependent coupling pairing of two completely smooth and unprofiled faces offers apparently an ideally precise and motion-free fixation while having the smallest closure path and opening path. This force-matching dependent coupling pairing requires however a completely impracticable large closure torque and opening torque for achieving a sufficient loadability, whereby finally even the immediate coupling pair itself loses again increasingly in quality.
The state of the art shows in a similar context a geometrically-caused relative increase in the size of the pair surface in the form of a ball-shaped body according to the European printed patent document EP 0 490 812 Bl (claims 6 and 7 as well as drawing, FIGS. 1-13), wherein one of the surfaces carries in addition a material-proper profile based on so-called bolting fibers, or alternatively, an anti-sliding coating. The two measures improve in fact the adhesion of the two pairing surfaces relative to which other, which however shows only that the designated hinge coupling is forced-matchingly constructed. Relatively high closure forces and opening forces as well as a relatively large volume of components carrying the coupling surfaces remain therefore in principle indispensable.
In this connection, a device for the external fixation of bone fragments has become known from the German printed patent document DE-OS 37 22 595 A1, which device considerably reduces the undesired clamping resistance of the movable and lockable telescope, operating as guiding columns of the fixator, based on surface hard-material coatings of an extraordinarily high hardness and low frictional coefficient, wherein a diamond-type carbon coating is proposed for this purpose in claims 1 and 2. This patent reference as well is clearly directed to the generally valid, urgent basic requirement for a reasonable, sensible kinematic, adjustable and effective, "well-running" fixator which would prevent jolt-like motions which could by all means lead to new injuries in the region of the fracture and which can impair, deteriorate, and worsen the healing process.
An important goal of the proposal according to German printed patent document DE-OS 37 22 595 is therefore a reliable and controlled readjustment of the fixator under compression load, which is only possible under stable low internal friction influence. The implicit essential aspect overlaying this is that the diamond hard-material coating is employed here for a decrease of the internal friction of the sliding surfaces of medical equipment and apparatus, which exhibits a broad competing spectrum of application of diamond coatings without a favorable priority. Furthermore, shape-matching pairings of surfaces, which furnish a relatively solid and visually controllable coupling connection based on profiles, formed on two sides like wedge teeth and disposed engaging each other on opposite sides, are still widely employed in clinical practice. Objectionably large closure paths and opening paths are required here by the relatively small, even though practically very differentiated closure forces and opening forces depending on the profile depths and the flank angle of the profiling, wherein the objectionable large closure paths and opening paths are additionally and regularly associated with an offset angle of the coupling surfaces both during the fixation as well as in particular during the defixation up to a size of a full profile spacing. Compare PCT WO 92/13496, FIGS. 3 and 4; in addition DE-OS 38 02 833 A1, FIG. 2 as well as column 3: "toothed annular face 17" as well as in particular journal: OP-Journal No. 3, Volume 11, December 1995, p. 373, SYNTHES, pictures to "the small fixator".
A pure force matching with a shape-matching component is in addition expressly indicated in the German printed patent document DE-PS 37 27 400 Cl in connection with the fixation of tangentially disposed cylindrical rods with outer threads, column 2, lines 13-28, which represents merely a geometrically critical tensioning of peripheral thread sections according to the solution of FIGS. 1 and 2. Therefore, the express claim of German Patent DE-PS 37 27 400 Cl remains uncovered in the solution provided.
All previously recited, subdivision-caused form-matching connections operate in fact sufficiently under the influence of a legitimate external load, they are however completely incapable to enter such a shape-matching coupling under the exclusion of illegitimate, coupling-internally induced loads.
A human medical compatibility of these engagement dependent, shape-matching couplings is therefore in general not recognizable for a surgical primary fixation in the course of a repositioning, such as in particular as sensitive defixation in the course of a postoperative dynamization, based on the already described claim of internal tension-free and point-precise coupling.
Therefore it appears to be imperative to define and to satisfy by way of invention an apparently buried requirement of the state of the art.
All previously described solutions of the state of the art are compromise-oriented selection decisions relative to their closure configuration, which selection decisions are characterized by nature by an equipment-specific weighing of the available functional criteria and technical parameters and which therefore deliver neither a generally satisfying solution nor a recognizable concrete suggestion for a qualitatively advancing new solution.
According to a more remote connection with the present invention, reference is made to long known, manual gripper instruments, such as two-armed tweezers for medical, in particular, surgical purposes, where the inner sides of the tweezers are covered with a diamond grain layer for improving the adhesion capabilities and the gripping capabilities as well as for a decrease of the subjective support force and cohesion. Already the German petit patent DE-Gbm 1 794 844 shows tweezers for medical use, wherein the inner faces of the front ends of the arms exhibit a diamond application or similar roughening.
The German printed patent document DE-OS 32 01 616 A1 describes foreign-body tweezers with two gripper tips plated or coated with the diamond dust in order to remove foreign bodies, in particular glass pieces or glass splinters, easily and with a light, minimal hand motion from the body of a human being or of an animal. Similar pronouncements are also contained in the German petit patent DE-Gbm 84 06 785.3 for tweezers for surgical and cosmetic purposes. Finally, the German petit patent DE-Gbm 85 12 734.5 describes precision tweezers, wherein at least one of the oppositely disposed jaw inner sides is formed with a grain layer of diamonds or of cubic crystalline boron nitride in a region of its clamping zones, in order to exceed the clamping effect of mechanical roughnesses and in order to penetrate with the grain tips into the surface of the object to be fixed or gripped. The extraction of teeth and of roots of teeth, as well as a removal of tissue, a removal of foreign bodies, and osteopathic surgical procedures are mentioned in this connection. Finally, the German petite patent concludes that the novel coating of the mouth of the tweezers in the region of the clamping zone is important for a secure and injury-free fixation of a part to be gripped.
Thus, it is common to all the recited instruments, that their two coated gripper arms are movable approximately within the arcuate measure of a preferably common swivel radius, and that the gripper arms form a tangent nearly planar parallel to the surface of an independent, regular non-metallic third body in a final operation position or temporarily penetrate the third body with their grain layer from two sides, in order to release the third body after a manual manipulation. A direct and immediate pairing of faces of the two coated metallic inner sides, which leaves the stated principle of an instrumental gripper coupling, is both strange and valueless in this context suggesting the concrete purpose determination of the tweezers. In addition, a direct and immediate face pairing is additionally technically without effect based on a two-sided coating of the arms, relative elastic arm cross-sections, as well as labile and not play-free swivel center points of the arms. Such further considerations relating to a radical reduction of the described function principle of coated gripper arms of tweezers in the sense of a static pairing of faces of their coated surfaces, possibly by a necessarily replacementless elimination of the independent gripper object itself, are therefore not only not suggested, but instead already suppressed or refuted in their premises.
The access to such, up to now unknown, aspects of diamond-coated plane-parallel surfaces at all, is therefore only possible by way of a not patent-preventing "ex-post facto analysis" under substantial incorporation of the present invention.